1. Field of Invention
The invention relates to a device for the production of tubes or sections of tubes, from which bags can be manufactured, wherein the tubes or sections of tubes have at least one layer of material, preferably a layer of paper.
2. Description of the Prior Art
The starting material for bags, particularly paper bags, is typically made available as webs wrapped around rolls. In the device named above, tubes or sections of tubes are produced from one or multiple webs by means of unrolling the web in an unwinder and subsequently providing the same with an application of glue in an edge region thereof (longitudinal gluing). A paste wheel serves this purpose. This is carried out in a device for the provision of at least one edge region with glue. The term “glue” is hereby used as an abbreviation meaning all types of adhesive. Following application of the glue, both edges of the web are turned around in the tube forming device in such a manner that the edges overlap each other and the application of glue bonds the overlapping edges. A tube machine as well as a device for providing at least one edge region with a glue, wherein a paste wheel is provided in the same, are disclosed in the publication DE 10 2007 032 401 A1.
Next, the tubes formed in this manner are typically isolated, either by means of a flush-cut knife or in a tearing station in which sections of tube are torn from the tube. In the latter case, lines of attenuation, for example perforations, have been inserted into the web already prior to the gluing process.
Next, the pieces of tube are processed into bags in a separate device.
Frequently, paper bags are not just made of one, but rather several layers. As such, bags for construction materials are made of an outer and an inner paper layer, and a (plastic) film layer lying between the paper layers. In order to increase the mechanical strength of these bags, the individual webs are arranged with a slight offset, such that each individual web can be provided with a longitudinal gluing, and subsequently each web can be bonded to itself.
Such bags are sufficiently strong. However, a problem arises when such bags are filled. Air is introduced during the filling process, and must be able to escape from the bag. This is because the bag could otherwise burst. In order to enable the escape of air, the tubes or sections of tubes are provided in the tube machine with channels through which air can move. This is done by applying perforations to the individual webs, wherein the perforations are sufficiently small for air, but not for the product, to escape. Conventional needle roller arrangements are used for this purpose, as presented in DE 195 44 330 A1, for example. The individual webs are arranged in such a manner that each of the perforations are offset to each other, in order to enable the escape of air while preventing the escape of the product filled in the bag. Such air vent perforations are not possible for single-layer tubes, because these would also allow the escape of the product.
The perforation process by means of needle rollers is complex. First, the construction costs, and therefore the sales price, of such a device are relatively high. Second, in the event that a change in the perforation scheme is desired, either the needles of the roller, or the needle roller itself, must be switched out.